Another distinguishing factor between Rackspace Cloud and EC2 or Linode are bandwidth caps. Rackspace limits outbound public network throughput to 10mbps for 256mb instances to 70mbps for 16gb instances. EC2 and Linode both provide an uncapped GigE Internet uplink for instances of any size.
http://cloudservers.rackspacecloud.com/index.php/Frequently_...